1. Field of the Invention
The present invention relates to an operation apparatus for a press, and particularly to an operation apparatus for a press in which simplification and cost reduction of the apparatus are achieved while ensuring a fail-safe characteristic.
2. Related Art of the Invention
In a system of a recent press, there has been provided such a safety function that a slide of the press (i.e., movable part of the machine side) can be automatically stopped if there occurs such a situation danger for an operator, and the operation of slide is permitted only when such a safety function is guaranteed to be normally operating. Examples of such conventional presses include one described in U.S. Pat. No. 5,285,721, which has been proposed by the present applicant.
In such a conventional operation system, there are used four signals P.sub.1 to P.sub.4 for indicating slide positions such as shown in FIG. 15, so as to realize the aforementioned safety function of the press. Namely, by utilizing these four signals P.sub.1 to P.sub.4, it is monitored as to whether the slide, after its elevation, has stopped within a predetermined range near the top dead center or not (overrun monitoring function), in order to confirm the brake performance; and the actuation of slide is permitted only when the brake performance is confirmed to be normal. To monitor the overrun, it is confirmed as to whether an operation button is turned OFF during the slide elevating process (confirmation of operation button OFF). In the above, the signals P.sub.1 to P.sub.4 are indicated by the crank angles corresponding to respective slide positions.
The signal P.sub.1 has logical value "1" within a range where the crank angle .theta. is from 340.degree. to 15.degree. and this range represents a range where the slide is to stop. Namely, the signal P.sub.1 is for confirming as to whether the slide, after its automatic elevation, has stopped by the crank angle 15.degree..
The signal P.sub.2 has logical value "1" within a range where the crank angle .theta. is from 345.degree. to 300.degree., and this signal P.sub.2 represents: a brake-performance-guaranteed lowering-motion-actuation starting point in case of slide lowering; and a range up to stoppage of automatic elevation of the slide. When this signal P.sub.2 has just become logical value "0", the slide elevation should be stopped.
The signal P.sub.3 has logical value "1" within a range where the crank angle .theta. is from 180.degree. (bottom dead center) to 350.degree., and this signal P.sub.3 represents a range of automatic elevation permission for the slide. In fact, the automatic elevation of slide is restricted at the crank angle of 300.degree. represented by the signal P.sub.2. Namely, the actual elevation permission range for the slide is the range (from 180.degree. to 300.degree.) in which both of signals P.sub.2 and P.sub.3 have logical value "1".
The signal P.sub.4 has logical value "1" within a range where the crank angle .theta. is from 270.degree. to 240.degree., and this signal P.sub.4 represents a range in which it is memorized and held that the operation button is turned OFF during the slide elevating process. When the operation button is turned OFF after passing over 270.degree. in the elevating process, this OFF confirmation signal is memorized and held up to 240.degree. in the next stroke.
Based on a generation state of such four signals P.sub.1 to P.sub.4, the aforementioned overrun monitoring is performed for each one cycle of the slide operation, so that the safety at the time of slide actuation is guaranteed by assuming the brake performance normality to be a prerequisite for the next slide actuation. In the above, the monitoring result of overrunning is utilized as a data for judging that the brake performance was normal at the last operation, even when the slide is stopped during slide lowering process. As such, it is required to memorize the monitoring result until just before this result is reconfirmed in the slide elevating process. Thus, in the aforementioned conventional apparatus, there is used a fail-safe self-hold circuit for memorizing the monitoring result.
However, the aforementioned conventional operation apparatus for a press is constituted such that a part of the slide position signals for monitoring is utilized as information for controlling. As such, there is not separation between the controlling system for executing the operation control such as actuation/stopping of slide and the monitoring system for monitoring the functions for ensuring safety, and rather, the monitoring system is integrally incorporated into the controlling system. Thus, not only the monitoring system but also the whole of controlling system have been required to be constituted in a fail-safe manner, causing that the number of required slide position signals becomes numerous so that the constitution of controlling system is complicated.